In the prior art, impregnated instruments which are used for cutting or polishing only have a single degree of abrasiveness throughout the work surfaces of the instruments. Thus, when, for example, a dentist must prepare a margin on a tooth, a first instrument must be used having a coarsely abrasive surface so that material may be removed from a crown, for example, to provide the proper configuration whereupon a second instrument with a fine abrasiveness may be used to polish the areas where the coarsely abrasive tool was used to remove material. Thus, a need has developed for dental instruments wherein each instrument includes regions of unique differing abrasiveness, which regions are adjacent one another and merge together at an interface.
Applicants are aware of the following United States patents:
U.S. Pat. No. 2,453,696 to Brooks PA1 U.S. Pat. No. 4,019,254 to Malmin PA1 U.S. Pat. No. 4,190,958 to Martin, et al. PA1 U.S. Pat. No. 4,518,356 to Green
None of these patents teaches the concept of differing abrasive surfaces on a single tool although both Malmin and Martin, et al. disclose tools having abrasive areas and areas without abrasiveness. In applicant' view, a tool with abrasive and non-abrasive areas is no different than a tool with a single abrasive property throughout since neither tool provides the possibility of treating a tooth surface with two degrees of abrasiveness on a single tool.
U.S. Pat. No. 4,338,748 to Elbel discloses a metal machining grinding tool having matrix bonded abrasive grains having a hardness which varies over the grinding area. The present invention is believed to distinguish from the teachings of this patent as teaching different degrees of abrasiveness in different regions of a single tool rather than different degrees of hardness.
Further, a product is known to applicants which is manufactured by the 3M Company and which comprises an elongated flexible plastic strip having aluminum oxide coatings at each end separated by an uncoated central portion with these coatings being in two different degrees of abrasiveness. The present invention is believed to clearly distinguish from the teachings of this product as including surfaces of differing degrees of abrasiveness which are immediately adjacent one another and which merge into one another.
Finally, German Gebrauchsmuster 8411017 discloses an instrument in FIG. 3 which includes a finely abrasive surface 18 and a coarsely abrasive surface 16 meeting at a jagged interface. The present invention is believed to be distinct from the teachings of this document since the present invention defines a clear transition zone between regions of differing abrasiveness which makes the present invention easier to use and more effective than the invention disclosed in the German document.